Railway trucks utilizing side frames connected by spider shaped members extending inwardly therefrom or other transversely disposed connecting members are used extensively to support car bodies. Such trucks are adapted to receive such structures as bolsters, air suspension springs and the like. Also, mountings to receive the wheel axle units are provided with the mountings designed to receive primary suspension springs and journal bearings therein.
Generally, trucks used heretofore have been designed in accordance with the particular requirements of the car body. For example, particular car bodies may be designed to carry a wide range of different loads ranging from very heavy loads to relatively light loads. In many cases heretofore, the trucks used to support the car bodies were either custom designed or, if such trucks were close to the requirement, had to be substantially modified.
The modifications required in the trucks have generally related to the primary suspension springs requirements. Different loads require different size springs at different locations on the truck frame. Also, often the wheel sizes and journal bearings make it necessary to relocate the journal bearings with respect to the truck frame.